Removal of some heavy metals onto mechanically activated fly ash: Modeling approach for optimization, isotherms, kinetics and thermodynamics

This study was recommended for the purpose of showing that mechanically activated fly ashes can be firstly used as an adsorbent for the removal of some heavy metals such as Cu(II), Mn(II), Ni(II), Pb(II) and Zn(II) from aqueous solutions. And with the idea that the adsorption capacity of fly ash can be modified by increasing the surface activity with mechanical activation, adsorption properties of activated fly ash samples were examined. Adsorption experiments were conducted on both fly ash samples. The optimizing of process parameters was evaluated employing response surface method (RSM) and adsorption mechanism can be explained by the quadratic model. The activated fly ash showed higher removal percentage (96% (w/w)) of all metals than the raw fly ash under the same experimental conditions. A pseudo-second order kinetic model fitted the adsorption data well. Moreover, the adsorptions of heavy metal ions on raw and activated fly ashes fit the Langmuir isotherm very well. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) were showed that the adsorption process is suitable, spontaneous and endothermic. The adsorption/desorption behavior of a multi-metal mixture on raw and activated fly ashes was firstly investigated. The adsorption/desorption percentages of Cu(II) and Pb(II) ions were higher than other ions. Mechanical activation results in decrease in particle size, increase in surface roughness and agglomerated particles as evident by characterization using XRD and SEM techniques. The results indicated that the heavy metal pollutants of aqueous solutions could be reduced using activated fly ash as a low-cost, available and waste adsorbent.